( Z)-α,β-Unsaturated esters can be stereoselectively synthesised in one pot under mild conditions and in good yields, by the hydrostannylation of alkynyl esters followed by Stille cross-coupling with aryl iodides.
The Stille coupling of (E)-α-stannyl-α,β-unsaturated esters with alkynyl bromides in DMF in the presence of Pd(PPh3)4 and CuI gave (Z)-2-ethoxycarbonyl-1,3-enynes in good yields. The latter underwent the palladium-catalysed hydrostannylation with tributyltin hydride in THF at room temperature to afford (1E,3E)-2-ethoxycarbonyl-3- stannyl-1,3-dienes in good yields with high regio- and stereoselectivities.
(E)-α-Stannyl-α,β-unsaturated esters underwent an iododestannylation reaction to afford (E)-α-iodo-α,β-unsaturated esters, which reacted with (E)-alkenylzirconium(IV) complexes produced in situ by hydrozirconation of terminal alkynes in the presence of Pd(PPh3)4 to afford stereoselectively a variety of 1,3-dien-2-yl esters in good yields.